1. Field of the Invention
The invention relates to the field of Micro Opto Electro Mechanical Systems (MOEMS) devices and in general to commercial micro systems technologies (MST) for optical communication.
2. Description of the Prior Art
Adaptive optics is a method for removing the blurring of images caused by changing distortions within optical systems. Turbulence in the Earth's atmosphere causes blurring of astronomical images. In an analogous manner internal imperfections and fluids in the eye cause blurring of images striking the retina.
Adaptive optics is a method for removing the blurring of images caused by changing distortions within optical systems. Turbulence in the Earth's atmosphere causes blurring of astronomical images. In an analogous manner internal imperfections and fluids in the eye cause blurting of images striking the retina. The use of adaptive optics allows ground based telescopes to see as clearly as if they were in space, and these techniques, when used to look at the retina of the human eye, dramatically sharpen images of the retina. Although adaptive optics was suggested for astronomy in the 1950s, only today are the requisite technologies (optics, computers, lasers) mature enough for adaptive optics to make an important impact on astronomy and vision science. Adaptive optics for astronomy on large telescopes promises a spectacular improvement in resolution, by factors of 10 to 30. Large ground-based telescopes using adaptive optics can even exceed the performance of the Hubble Space Telescope and at much lower cost. Adaptive optics for vision science promises to correct the aberrations of the eye and to provide a powerful tool for understanding the structure and development of cones and rods in the living human retina. It also holds the promise of diagnosing tiny retinal defects before they become large enough to threaten our person's vision. Adaptive optics systems require the marriage of several very advanced technologies—precision optics, wavefront sensors, deformable mirrors, and lasers-all tied together by high-speed control systems. In order for an optical system to approach its diffraction limit, it is necessary to correct the wavefront of the light to remove distortions that deviate the system from the ideal. Incorporating a deformable mirror can do this: i.e. a reflecting element that has on its backside an array of actuators that push and pull at the mirror to compensate for wavefront distortions. In a space based system, where energy and size considerations are paramount, it is highly advantageous to make this system small, compact, robust and energy efficient. Piezoelectrically actuated MEMS are needed from the point at which the benefit of precision spatial control offsets the added complexity of microfabrication. Lightweight, low power implementation of microfluldic pumps and micropositioners based on piezoelectric actuation can be incorporated into chromatographic/interferometric instruments and miniature propulsion systems. Recent studies indicate promising piezoelectric properties of some new thin film material compositions at ambient temperatures. Also piezoelectrically actuated deformable mirror arrays are rapidly becoming the next largest commercial MEMS applications, finding widespread use in telecommunication fiber-optic routers and advanced projection displays. Pixelated PZT actuated mirror arrays have been developed in the commercial arena.
MEMS technology is used to make ultra miniaturized and high-precision components for the micro optical subsystems for both conventional and cryogenic applications. Currently available continuous membrane deformable mirrors are not capable of generating 12 μm stroke actuation, while providing an excellent optical figure with modest actuation voltages.
Most currently available deformable mirrors are made with lead zirconium titanate (PZT), which degrades in optical quality over time, bringing hysteresis, creep, and capacitive heating effects, which are not satisfactory to meet NGST requirements for an optical figure which remains stable for a period of weeks. The electrostrictive lead magnesium niobate (PMN) technology at Xinetics Inc. has been demonstrated with excellent surface stability for a period of weeks (±2 μm stroke with 7 mm actuator spacing). Micromachined designs have been developed by several research groups to improve the deformable mirror technology and offer the potential to be scalable and cost effective. Segmented mirrors have been created with individual pixel tip/tilt capability. Micromachined continuous membrane deformable mirrors have been previously fabricated by Delfi and JPL. Both have excellent surfaces but the mirror membranes have high cross-talk between individual pixels. An electrostatically actuated, surface micromachined deformable mirror has been demonstrated. This micromachined deformable mirror has a continuous mirror backed by parallel plate actuators, which is fabricated using the surface micromachining technology embodied in the MUMPS. Restriction to the MUMPS creates design limitations and marginal surface quality, which in turn limits the applicability of this approach. A more recent effort has produced a continuous single crystal silicon deformable mirror, which is also electrostatically actuated.
None of the continuous membrane deformable mirrors described above, however, are capable of generating 12 μm stroke actuation with modest actuation voltages.
However, what is needed is a new design for the materials, structures and fabrication method is necessary to meet the requirements of imaging adaptive optics for the vision science.